The simian immunodeficiency virus of macaques (SIV), a T-cell tropic lentivirus closely related to the human immunodeficiency viruses (HIV), induces an AIDS-like disease in juvenile rhesus monkeys. This virus and the rhesus monkey will be utilized as an experimental model for the study of AIDs. This model will be employed to: I. Characterize the CD8+ cellular response of the rhesus monkey to SIV. II. Assess the effects of SIV infection on rhesus monkey bone marrow cellular maturation.